A simple test application is given in OBS to create a scene and display it in windows:

int WINAPI WinMain(HINSTANCE instance, HINSTANCE prevInstance, LPSTR cmdLine,
		int numCmd)
{
	HWND hwnd = NULL;
	base_set_log_handler(do_log, nullptr);

	try {
		hwnd = CreateTestWindow(instance);
		if (!hwnd)
			throw "Couldn't create main window";

		/* ------------------------------------------------------ */
		/* create OBS */
		CreateOBS(hwnd);

		/* ------------------------------------------------------ */
		/* load modules */
		obs_load_all_modules();

		/* ------------------------------------------------------ */
		/* create source */
		SourceContext source = obs_source_create("random",
				"some randon source", NULL, nullptr);
		if (!source)
			throw "Couldn't create random test source";

		/* ------------------------------------------------------ */
		/* create filter */
		SourceContext filter = obs_source_create("test_filter",
				"a nice green filter", NULL, nullptr);
		if (!filter)
			throw "Couldn't create test filter";
		obs_source_filter_add(source, filter);

		/* ------------------------------------------------------ */
		/* create scene and add source to scene (twice) */
		SceneContext scene = obs_scene_create("test scene");
		if (!scene)
			throw "Couldn't create scene";

		AddTestItems(scene, source);

		/* ------------------------------------------------------ */
		/* set the scene as the primary draw source and go */
		obs_set_output_source(0, obs_scene_get_source(scene));

		/* ------------------------------------------------------ */
		/* create display for output and set the output render callback */
		DisplayContext display = CreateDisplay(hwnd);
		obs_display_add_draw_callback(display, RenderWindow, nullptr);

		MSG msg;
		while (GetMessage(&msg, NULL, 0, 0)) {
			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}

	} catch (char *error) {
		MessageBoxA(NULL, error, NULL, 0);
	}

	obs_shutdown();

	blog(LOG_INFO, "Number of memory leaks: %ld", bnum_allocs());
	DestroyWindow(hwnd);

	UNUSED_PARAMETER(prevInstance);
	UNUSED_PARAMETER(cmdLine);
	UNUSED_PARAMETER(numCmd);
	return 0;
}

About the call of obs:

1.CreateOBS calls obs_reset_video and passes in a parameter obs_video_info, which is a structure:

	struct obs_video_info ovi;
	ovi.adapter         = 0;
	ovi.base_width      = rc.right;
	ovi.base_height     = rc.bottom;
	ovi.fps_num         = 30000;
	ovi.fps_den         = 1001;
	ovi.graphics_module = DL_OPENGL;
	ovi.output_format   = VIDEO_FORMAT_RGBA;
	ovi.output_width    = rc.right;
	ovi.output_height   = rc.bottom;

Includes the size of the display device and the rendering device DL_OPENGL used

2.obs_load_all_modules Load obs-related modules including plug-ins

3.obs_source_createc creates a source

4.obs_scene_create creates a scene

5.obs_scene_add binds source and scene

6.obs_set_output_source sets the source as the output object

7.DisplayContext display = CreateDisplay(hwnd);

obs_display_create draws the rendering result to the window

8.obs_display_add_draw_callback(display, RenderWindow, nullptr); can take over the drawing process of OBS